1. Field of the Invention
The present invention relates generally to an exchangeable multiplunger transfer molding die apparatus and more specifically to a die apparatus exchangeably mounted on a multiplunger transfer molding machine without exchanging plungers and a constant pressure applying device.
2. Description of the Prior Art
To seal semiconductor devices with resin, a semiconductor device is set within a cavity formed in a metallic die and then a heated soft resin is inserted into the cavity under pressure to harden the inserted resin around the semiconductor device. In the above-mentioned process, transfer molding method is usually adopted. In this method, since resin is fed to dies through slender gates, heating or hardening of products is uniform; hardening time is short; dimension precision is high without damaging or deforming semiconductor devices.
FIGS. 1(A) and 1(B) illustrate an example of the transfer molding method, in which heated resin is pressurized by a plunger PL and fed from a supply pot SP to cavities CA through an auxiliary liner AUL and gates GA to surround products by resin remaining within the cavities CA. In this method, however, since other residual resin material is not available again, there exists a problem in that the yield of resin material is not satisfactory.
To overcome this problem, so-called multiplunger transfer molding dies have been proposed as shown in FIG. 2(A), in which a number of supply pots SP are arranged in the vicinity of cavities CA and connected to the cavities CA via gates GA and further each plunger PL is provided for each supply pot SP to supply resin material into the cavities in order to reduce material not used.
An example of a multiplunger transfer molding die will be described in further detail with reference to FIG. 2(B) under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
In the above multiplunger transfer molding die, it is possible to continuously molding the same products effectively. However, it is necessary to exchange the molding die whenever other products are required to be molded. In the multiplunger transfer molding die, since the number of cavities formed in a die is different according to products to be molded and therefore the pitch of the resin supply pots SP is also different between products, it is necessary to change the die and simultaneously the pitch of the plungers each for applying pressure to material in each supply pot SP.
However, it is not easy to change the pitch of the plungers and it takes much time to set new plungers to the molding machine, because it is very troublesome to remove the constant pressure applying device from the machine and correctly locate the multiplunger again on the molding machine in concentric positional relationship to the supply pots.
Conventionally, therefore, whenever new products are required to mold, the entire die apparatus is completely exchanged to reduce die setting time. However, when a number of expensive die apparatus are prepared, there arise other problems such that the economic loss is great; the die storage space is broad; and the die exchange work is inefficient, thus increasing molding cost and decreasing molding productivity.